Conventionally, a wheel loader is known as a working machine. In a wheel loader, an attachment such as a bucket or the like is provided at an end of a boom pivoted on a vehicle body, and the boom is provided in a manner movable up and down by a boom cylinder, and the bucket is driven via a Z-bar link.
The Z-bar link includes, as shown in FIG. 35, a bell crank 11 turnably pivoted on a substantially central portion of the boom 10, a tilt cylinder (refer to chain lines) connecting an end of the bell crank 11 and the vehicle body (not shown), and a connecting link 13 for connecting the other end of the bell crank 11 and a back side of the bucket 20.
Incidentally, in FIG. 35, the boom cylinder and the tilt cylinder are not shown to simplify the figure. In addition, although the pivoted position Z of the tilt cylinder on the vehicle body (pivot position) is drawn on the boom 10 in the figure, the actual pivot position is on the vehicle body (not shown), not on the boom 10. In FIG. 35, postures of the bucket 20 at a ground position, an intermediate position, and a top position are shown.
In the wheel loader having such configuration, the bucket 20 is positioned close to the ground position to perform digging work, and to the intermediate position or the top position to dump onto a truck therefrom.
Besides the digging work, the wheel loader may be used to scoop mud, animal waste or the like. In this case, as shown in FIG. 36, the bucket 20 is tilted at the ground position so that the mud or the like having fluidity is not spilt, thereby efficiently performing the scooping work.
As the wheel loader, a wheel loader having improved angular characteristics in which the pivot position of the tilt cylinder on the vehicle body is set at a prespecified position and thereby an attachment angle is kept substantially constant from the ground position to the top position of the bucket is also known (for instance, Patent document 1).
Movements in this configuration are simplifiedly drawn in FIG. 9.
Further, there has been also known that the bell crank constituting the Z-bar link is tilted toward the attachment side (for instance, Patent document 2).
Concretely, as shown in FIG. 37 and FIG. 38, relative to a line L1 connecting a pivot position Y on the boom 10 and a pivot position X on the connecting link 13, a line L2 connecting a pivot position W on the tilt cylinder 12 and the pivot position Y of the bell crank 11 of the wheel loader is inclined toward the bucket 20 side.
In addition, a wheel loader in which a fork is combined with the Z-bar link is also known (for instance, Patent document 3).
As shown in FIG. 39, according to this wheel loader, the bucket 20 may be replaced with the fork 30, and when replacing, the tilt cylinder (not shown) is a little extended so that the fork 30 can be attached. Namely, the extension amount of the tilt cylinder is, as shown in the chain double-dashed line, equivalent to an offset angle α of the bucket 20, and the fork 30 is attached to the connecting link 13 at this position.
Accordingly, even in the wheel loader using the Z-bar link, the attachment angle from the ground position to the top position is kept substantially constant, where the angle characteristics is improved, so that work using the fork 30 can be performed.
On the other hand, as another configuration of the wheel loader, there is a parallel link type as shown in FIG. 40. In the parallel link configuration, a lower end of a tilt lever 19 (a lower end in the state shown in the figure) is pivoted on the boom 10, the connecting link 13 is attached so that an upper end of the tilt lever 19 and a back side of the fork 30 are connected, and the tilt cylinder 12 is attached so that an intermediate portion of the tilt lever 19 and the vehicle body (refer to the chain double-dashed line) are connected, and thereby, the boom 10 and the connecting link 13 are disposed in parallel to each other.
With the wheel loader using the parallel link, even when the boom 10 is rotated upward, since a posture of the fork 30 can be kept constant without changing the advancement and retraction amount of the tilt cylinder 12, transporting and lifting/unloading work of cargos can be stably performed.    Patent document 1: Japanese Patent Laid-Open Publication No. HEI 11-343631    Patent document 2: U.S. Pat. No. 4,154,349; specification    Patent document 3: Japanese Patent Laid-Open Publication No. SHO 63-22499